1. Field of the Invention
The invention relates to a connector assembly and to a wellhead assembly provide with such a connector assembly.
2. Description of the Related Arts
It is known from U.S. Pat. No. 5,558,532 to provide an underwater wellhead assembly comprising a vertically oriented tubing hanger disposed in a spool body, and a connector assembly comprising a first connector part in the form of a plug body and a second connector part in the form of a receptacle for the plug body. The receptacle is arranged in the tubing hanger with its axis horizontal and the plug body is mounted by a carriage horizontally reciprocatable between a forward position in which the connector parts are connected and a retracted position in which the connector parts are disconnected. In the retracted position the plug body is fully withdrawn from the tubing hanger so that it is then possible to remove the tubing hanger, together with the receptacle, vertically from the spool body and to take it to surface for repair or modification. Each time the tubing hanger is returned to the spool body it has to be accurately located so that the connector parts are in alignment with each other. However, because of manufacturing tolerances exact alignment is not always achieved, and there may be a lateral offset between the longitudinal axes of the connectors (lateral misalignment), or an angular misalignment between the axes, or a combination of the two. If there is misalignment, there may be a problem in that the plug body cannot properly engage the receptacle during the forward movement of the carriage.
To deal with this problem, we have previously proposed a mounting arrangement for the plug body on the carriage which allows lateral movement of the plug body relative to the carriage, and limited pivotal movement about a vertical axis only. This mounting arrangement consists of a pair of radially outwardly projecting circumferential flanges on the plug body, the flanges being longitudinally spaced from each other, and a split ring on the carriage projecting radially inwardly into the space between the flanges. An O-ring is disposed around the plug body radially inwardly of the split ring. The plug body is able to move laterally relative to the carriage, if necessary to correct lateral misalignment as it engages in the receptacle, by deforming the O-ring. In addition, because the split ring projects into the space between the plug body flanges at the top and the bottom of the plug body, but not at the sides, a small amount of pivotal movement about a vertical axis is possible to correct angular misalignment.
Such a mounting arrangement works well. In some circumstances, however, for example when the receptacle is arranged with its central longitudinal axis tangential to a circle about the central vertical axis of the tubing hanger (rather than radially of the tubing hanger), it is necessary to design the plug body and mounting with a relatively long portion of the plug body projecting forwardly of the mounting. The weight of the forwardly projecting portion creates a couple which increases friction at the mounting and thus restricts its ability to allow the plug body to move relative to the carriage during correction to correct any misalignment. Another possible cause of restricted movement at the mounting is the presence of sand or other debris, which may create a problem even if the forwardly projecting portion of the plug body is relatively short.
According to a first inventive aspect there is provided a connector assembly comprising first and second connector parts, the first connector part being mounted by a carriage reciprocatable between a forward position for connecting the connector parts and a retracted position for disconnecting the connector parts, wherein the mounting of the first connector part by the carriage is such as to permit pivoting of the first connector part in response to a force in any lateral direction on the first connector part and acting at a location forward of the mounting.
If there is misalignment of the connector parts when disconnected, as they are brought into engagement the first connector part can align itself with the second connector part. The pivotal mounting of the first connector part enables the correction in alignment to be achieved. Thus any tendency for the first connector part to become jammed during the connection process as a result of misalignment is reduced.
The lateral force may for example be horizontal or vertical, both of these being lateral to the longitudinal axis of the first connector part, or a combination of the two, depending on the direction of misalignment to be corrected. As discussed above, there may be a tendency for the first connector part to tilt downwardly, when disconnected, due to the weight of the portion of the first connector part projecting forwardly of the mounting. In such a situation, since the mounting can permit downward pivoting about a horizontal axis, its functioning will not be impaired by increased friction, as in the known mounting system. The downward tilting can be reversed as the first and second connector parts engage with each other and a correcting lateral (i.e. upward) force is applied by the second connector part to the first connector part.
Preferably, one of the connector parts is a plug body and the other a plug receptacle. In order to help correct misalignment during the forward stroke of the carriage, the plug body may have an externally chamfered nose whilst the plug receptacle may have an internally chamfered mouth. If there is misalignment, the chamfers allow the nose to engage in the mouth during the carriage forward stroke. It is preferred that the first connector part is the plug body and that the second connector part is the plug receptacle, although the reverse arrangement is possible
The connection to be made may be electrical (such as low power for gauges or other instrumentation or high power for powering equipment such as a down hole pump) or optical or a mixture of the two. A preferred connector, having first and second connector parts for use in the connector assembly, is described in GB-A-2 192 316.
Another cause of an initial angular misalignment of the first connector part, in addition to the downward tilting mentioned above, may be an eccentric load applied by a cable extending from the rear of the first connector part. In many cases, the problem of an initial angular misalignment is overcome, as the desired final orientation of the first connector part can be achieved by the application of a correcting lateral force by the second connector part as the two are brought into engagement. The pivotal mounting enables this to be achieved. However, in situations where the length of the first connector part projecting forwardly of the mounting is relatively long (as in the case for example of a non-radial entry to a tubing hanger mentioned above), there is a corresponding increased effect of any angular misalignment at the front end of the first connector part, where it first engages with the second connector part during the forward stroke of the carriage. In an extreme case, it may not be possible to achieve connection.
Preferably, therefore, the mounting is such as to centre and align the first connector part along a predetermined axis when the carriage is in the retracted position. Such an arrangement ensures that the first connector part is in the proper orientation relative to the carriage, despite any forces applied to the first connector part by its own weight or a cable connected to it. There may of course still be misalignment between the first and second connector parts, caused by misalignment of the carriage relative to the second connector part, but this will normally be small and readily correctable during the connection process.
Apart from an angular misalignment relative to the axial direction there may be a lateral offset and therefore preferably the mounting of the first connector part is such as to permit lateral movement of the first connector part relative to the carriage.
In a preferred arrangement the first connector part is resiliently mounted by the carriage. This can be useful in achieving a proper connection between the first and second connector parts. For example, the assembly can be designed such that the first and second connector parts are fully connected and seated against each other slightly before the carriage completes its forward stroke to the forward position, with the additional movement of the carriage being permitted by the resilience of the mounting. Thus the carriage can be arranged to move forward by more than the first connector part, reducing the chance that there will not be a proper connection because of manufacturing errors or because of debris preventing the carriage from completing its forward stroke.
The first connector part may be mounted in a block of resilient material, such as a solid rubber bushing. However, in certain uses of the connector assembly, such as in a wellhead, the resilient material would have to be tolerant of the well completion fluid (generally brine), of high temperatures (typically 145.degree. C. or more at certain times), and would preferably not be susceptible to compression set. It is therefore generally preferred to provide resilience by the use of one or more springs of steel or the like.
Preferably the first connector part has a bearing portion biased against an abutment of the carriage. Such a bearing arrangement should permit pivoting of the first connector part and preferably also will be such as to centre and align the first connector part when disconnected. This can be achieved if the bearing portion has a conical face engaging a conical face of the abutment. One conical face will be "concave", in the form of a cup, and the other will be "convex". The convex conical face will thus be able to "rock" within the concave conical face to provide the desired pivotal movement. Preferably, the convex conical face belongs to the first connector part and the concave conical face to the carriage, but the reverse is possible. By providing adequate lateral clearance between the bearing portion and the abutment, relative lateral movement will also be possible.
Advantageously, the bias of the bearing portion of first connector part against the abutment of the carriage is resilient, thus providing the mounting with its preferred resilience. Although the bearing portion could be biased rearwardly, e.g. by one or more springs, it is preferred that the bearing portion is forwardly biased.
Preferably, the bias is provided by a compression spring coiled round a shaft projecting rearwardly of the bearing portion and biasing the bearing portion forwardly against the abutment. This provides an economical use of space whilst also enabling some longitudinal play allowing the carriage to stroke forward by more than the forward movement required by the first connector part to achieve proper connection.
If the connection involves the mating of a single centrally located pin in a corresponding socket, then it may not be essential to maintain the first and second connector parts rotationally aligned when disconnected. Preferably, however, there is provided means for preventing rotation of the first connector part relative to the carriage about a longitudinal axis. This may for example take the form of a longitudinally arranged pin engaging in a corresponding hole.
In our known mounting arrangement described above, a cable protrudes from the rear end of the plug body, at an angle to the longitudinal axis and at an off-centre location. This can result in the cable applying a force to the plug body which causes it to be out of alignment with the carriage. In order to minimise such a problem, a preferred embodiment of the present invention comprises a cable extending axially and centrally from a rear end of the first connector part. It may be desired to form the cable to the rear of the first connector part into a coil about a longitudinal axis, in order to accommodate forward and rearward reciprocating movement of the first connector part. In this arrangement, since the deviation of the cable from the central axis first occurs behind the first connector part, it has a reduced potential for eccentric loading on the first connector part than in the known mounting arrangement.
The connector assembly is preferably an underwater or other severe environment connector assembly. It is envisaged that it will be particularly useful as part of a wellhead installation.
A preferred embodiment therefore comprises a wellhead assembly comprising a radially inner member, a radially outer member, and a connector assembly as described above, wherein the carriage and the first connector part of the connector assembly are carried by the radially outer member and the second connector part is carried by the radially inner member.
With such an arrangement, when the carriage is in the retracted position, the connector parts are disconnected and allow relative axial movement of the radially inner and outer members. The radially inner member may for example be a tubing hanger and the radially outer member a spool body.
In known connector assemblies there may in some circumstances be difficulties in withdrawing the carriage to the retracted position, for example due to a failure of an actuator for the carriage, or seizure of the carriage in its guide, or seizure of the connector parts in their connected condition. If this happens, it may be desired to try and recover one of the two members which carry the respective connector parts of the connector assembly, without recovering the other member. In the example mentioned above of a wellhead assembly, it may be desired to remove the tubing hanger from the spool body to take it to surface for repair or modification. If however the carriage cannot be retracted then the first connector part will normally prevent recovery of one of the members without the other, because it extends between the two when the carriage is in the forward position.
According to a second inventive aspect there is provided a connector assembly comprising first and second connector parts, the first connector part being mounted by a carriage reciprocatable between a forward position for connecting the connector parts and a retracted position for disconnecting the connector parts, wherein the first connector part comprises a weakened portion providing a reduced resistance to shear.
With such an arrangement the first connector part can if necessary be sheared at the weakened portion. Although this will result in the destruction of the first connector part, this may be a justifiable sacrifice if it enables recovery of a member carrying the first or second connector part. Thus, if the carriage and the first connector part are carried by a first member, and the second connector part is carried by a second member, then one of the members may be recovered, even if the carriage cannot be retracted, by shearing the first connector part.
The shear load may for example be reduced from an order of 20 tonnes to an order of 6 to 9 tonnes at the weakened portion.
In one embodiment, the weakened portion is located on the first connector part at a region adjacent to a front end of the second connector part when the connector parts are connected (the "front end" of the second connector part meaning the end nearest the carriage). Such an arrangement is useful for example if the second connector part is to be carried by a second member with its front end at the periphery of the second member, so that shear can occur at the periphery. It may also be useful if the second connector part is to be carried by a second member with its front end inwardly (i.e. rearwardly in relation to the second connector part) of the periphery of the second member. Shearing of the first connector part can then occur at the front end of the second connector part, inwardly of the periphery. However, in this latter disposition of the connector assembly, an alternative embodiment comprises the location of the weakened portion on the first connector part at a region rearwardly of a front end of the second connector part when the connector parts are connected (i.e. rearwardly in relation to the first connector part). For example, the weakened portion can be located at the periphery of the second member which carries the second connector part, so that shear can occur at this point.
The weakened part may be in the form of a peripherally extending groove in an outer wall of the first connector part. It may run transverse to the longitudinal axis, or at a non-perpendicular angle to the longitudinal axis, for example to correspond to the profile of the periphery of a second member as viewed in the direction of shear.
One of the connector parts is preferably a plug and the other a receptacle, with the plug being receivable in the receptacle to make a connection. Preferably, the first connector part is the plug and the second connector part the receptacle, although the reverse arrangement is possible.
It is expected that the connector assembly including a first connector part with a weakened region will be particularly useful as part of a wellhead installation.
A preferred embodiment therefore comprises a wellhead assembly comprising a radially inner member, a radially outer member, and a connector assembly comprising first and second connector parts, the first connector part being mounted by a carriage reciprocatable between a forward position for connecting the connector parts and a retracted position for disconnecting the connector parts, wherein the carriage and the first connector part of the connector assembly are carried by the radially outer member and the second connector part is carried by the radially inner member, and wherein the first connector part comprises a weakened portion providing a reduced resistance to shear.
If it is desired to remove the radially inner member from the radially outer member, this can be achieved even if the carriage cannot be retracted, by shearing the first connector part.